When a vehicle, such as a car, van or truck, tows a trailer there is a possibility under certain conditions for the trailer to oscillate or “fish-tail” behind the vehicle. This can be particularly problematic at high road speeds and during critical maneuvers such as lane changes and sharp cornering.
Vehicle-trailer combinations typically act like damped systems in which the magnitude of a damping co-efficient associated with the system dictates the rate at which oscillations of the trailer decay after it has been displaced from a neutral position behind the towing vehicle, e.g. by a gust of wind, etc. With such a system, the greater the vehicle's road speed, the lower the damping co-efficient of the vehicle-trailer system becomes. Thus, the system becomes increasingly unstable as velocity increases. This problem is exacerbated by the fact that, in recent years, increasingly stringent vehicle emission regulations have resulted in decrease in average vehicle weight and studies have shown that this decrease in vehicle weight has had an adverse effect of vehicle stability, particularly when towing a trailer.
Many vehicles are provided with Electronic Stability Control (ESC) (also known as Electronic Stability Programs (ESP) and Dynamic Stability Control (DSC)) which help improve vehicle stability. When such a vehicle tows a trailer, ESC can help to improve the stability of the vehicle-trailer system by methods such as selectively braking individual wheels of the vehicle. However, the presence of a trailer must be detected in order for ESC to be applied.
It is known to use an electrical connection to determine whether a trailer is connected to a vehicle to allow an electrical supply to the trailer rear lights. The current or voltage running through this electrical connection can be detected and used to indicate that a trailer is attached to the vehicle. However, modern LED technology has the disadvantage that the currents used are so low that reliable detection is difficult. Generally the detection of a trailer is done once at “key-on” and not thereafter so if a trailer is hitched/unhitched without turning the engine off then there will be no detection in a change of the trailer status. In addition there are events wherein the trailer electronics are connected but the vehicle is not towing, for example if bikes are attached to the rear of a vehicle in a manner that obscures the lights or registration it is common to use an auxiliary light board containing the registration plate attached to the rear of the vehicle or to the bikes in a viewable position so that the vehicle is in compliance with legal requirements. Such auxiliary light boards are generally connected to the trailer electronic outlet. Furthermore, this method does not give any information about the trailer.
It is also known to use sensors to detect any lag in yaw of the vehicle to determine whether a trailer is attached. Yaw is rotational motion of the vehicle about its vertical axis, resulting in a change to the direction the vehicle is pointing, i.e. to the left or right of its direction of motion. A trailer will affect the time between a change in steering angle and the resulting yaw; this lag can be used to detect whether a trailer is attached to the tow vehicle.
Another known method is to measure the drag on the engine torque due to the extra weight of the trailer.
These two latter methods, i.e. measuring the lag in yaw and the drag on torque, have the disadvantage that whilst they work well when the attached trailer is of sufficient mass/length to substantially alter the vehicle's character, it becomes difficult to distinguish the trailer attachment from noise as the trailer's critical dimensions are reduced. In addition other factors such as the drag on the vehicle due to the surface of the terrain may influence detection based on drag/engine torque. In addition, these methods can only be used to identify a trailer when the tow vehicle is moving but not when it is stationary.
It is an aim of the present invention to address disadvantages associated with the prior art.
A further aim of the present invention is to improve the detection rate of prior art methods.
A further aim of the present invention is to improve the accuracy of prior art methods.